Honestly I’m not sure, I’m also quite new to the fediverse. My guess is that being a parent comment, B wouldn’t see it, but if C was the parent and A the child comment, B would see only C.
Someone else explained this pretty well in an answer. If that guy is correct neither users from instance B nor C will see the comment from the A instance user. This is because the post is hosted on instance B. And A-B are not federated (because of the block from B’s side). This causes the comments from A to not be synched with B and therefore also not with C by proxy.
Honestly I’m not sure, I’m also quite new to the fediverse. My guess is that being a parent comment, B wouldn’t see it, but if C was the parent and A the child comment, B would see only C.
Someone else explained this pretty well in an answer. If that guy is correct neither users from instance B nor C will see the comment from the A instance user. This is because the post is hosted on instance B. And A-B are not federated (because of the block from B’s side). This causes the comments from A to not be synched with B and therefore also not with C by proxy.